Export blender scene as xml
Short answer: No. 

XML is per definition too broad to cover all the specific user cases one could imagine. 

OBJ and its material format MTL on the other hand are highly defined in their purpose. 

Even if there would be a OBJ/MTL to XML exporter, it's highly unlikely that it would meet all of your requirements. 

The long answer: Since OBJ and MTL are well documented, it might be easier to program a converter instead of an exporter.